1. Field of the Invention
This invention relates to electric arc furnaces. More specifically it relates to an extended arc furnace employing at least one electrode with an axial opening through which an appropriate gas, such as argon, may be introduced. Still more specifically the furnace embodies a vertical reaction chamber through which a particulate charge is fed by gravity into the extended arc zone and in its course through the reaction chamber is heated and, if desired, reacted.
2. Related Prior Art
The conversion of iron ore to iron is still being conducted primarily in blast furnaces. In spite of numerous attempts to design more simple equipment which is economical on a small scale for this purpose, blast furnaces are still being used to handle about 98% of the world's production of iron.
One attempted method to circumvent the use of the blast furnace for this purpose is known as the Strategic-Udy process. This involves the use of a large, substantially horizontal rotary kiln which performs the same fuel-burning and most of the ore-reduction operation which is effected in the blast furnace. The product is dropped continuously into an electric furnace to melt it for pouring into ingots. Here again the equipment is cumbersome and expensive to operate as evidenced by the fact that it has not been commercially adopted to any substantial extent.
Electric shaft furnaces have also been attempted in which the tuyeres at the bottom of the blast furnace have been replaced by an electric arc furnace to provide the heat for melting the reduced product after the conglomerate charge has passed downward through the reducing zone of the blast furnace-like vertical shaft. This has likewise met with little commercial success.
British Patent No. 1,102,900 suggests the use of a plasma torch furnace for reducing a conglomerate mineral charge in which the conglomerate charge has been moved downward and counter-current to a stream of reducing gases emanating from the plasma torch so as to preheat the charge and the reduction is effected in the slowly moving column by a reducing gas such as methane or other hydrocarbon through an annular passage surrounding the electrode or electrodes in the plasma furnace and directed so that the reducing gas is ionized before it passes into the conglomerate to perform its reducing function.
This process resembles blast furnace operation in that reducing gases are passed upward through a descending column of conglomerate iron ore and the reduction is performed in this descending column. In the blast furnace the reduced charge is being melted at the bottom of the column where intense heat is generated by combustion whereas in the process of the patent the reduced conglomerate charge is melted at the bottom of the column by the plasma torches. This process also has some of the disadvantages of the blast furnace because of the cumbersome, expensive equipment required. In this process the ore must be agglomerated, and the composition must be carefully controlled with a relatively high percentage of iron being present in the ore. Moreover plasma torches are expensive and difficult to maintain.
U.S. Pat. No. 3,834,895 shows another process using a plasma arc furnace. In that case, particulate iron-bearing material is dropped into the plasma from a hopper situated immediately above the furnace. A gas such as argon is fed into the furnace through an annular passageway surrounding either the hopper or the electrode. The gases are exited from the furnace through an outlet at the top of the furnace without coming into contact with the charge prior to entry of the charge into the furnace. The patentee stresses as novel the feature of collecting the melted iron at the bottom of the furnace and removing it in a molten form. No mention is made of a reducing operation nor is any reducing agent mentioned or provided for in the description of the process. Moreover no mention or provision is made for the removal of slag that would be produced in an ore reduction operation. Furthermore the arc is highly unstable.
U.S. Pat. No. 3,783,167 discloses a cumbersome mechanical device designed to produce an extended arc zone by moving an electrode or a plasma gun in a closed path so that the resultant arc would be moved into greater volume. In addition to being cumbersome and difficult to maneuver, this equipment is quite inefficient from an energy consumption aspect.